Assuming you can get composite video out of your iPad the "most available" option for an RF modulator is to use an old VCR. Most VCRs, even quite old ones, have composite in/out jacks for dubbing or connecting a video camera. Hook your iPod to the composite in jack (and the sound to the audio input jacks), the TV to the RF out jack via your matching transformer, and set the VCR to "video in" (or whatever it calls it).

Or you could get a stand alone RF modulator. They were still making them until not that long ago. (I have one in a junkbox I'm holding on to in case I ever find a retro TV I just can't pass up.)

BTW, don't be confused by what Unknown_k is referring to, which is bypassing the old RCA to antenna switchboxes used by game consoles. The output from said consoles was RF modulated, not the composite you'll get from the iPad adapter. A simple transformer won't make the conversion for you.